This study of the epidemiologic pathology of childhood brain tumors is divided into two parts; both are based on the same strategies. In an attempt to improve prognostic ability, first biopsy samples from site-specific brain tumors in childhood are coded for a large number of histologic characteristics under rigidly defined conditions (specific definition of each characteristic, simultaneous reading by two observers, etc.) without knowledge of clinical characteristics which are recorded separately. The prognostic information associated with each histologic feature is estimated by constructing life tables for each feature. Clustering among histologic and clinical features is sought as a formal way of defining syndromes with prognostic information. Secular trends for each feature are sought. Part A of this study is focused upon the dense cell tumors in the posterior fossa in children. Part B is for planning a consortium of pediatric institutions for a similar study of all childhood brain tumors.